Driveshaft rebuilding machines are known in the art and are sometimes called push-up machines. These machines essentially attach driveshaft end pieces to driveshaft tubes by press-fitting the end pieces to the tubes. One prior art configuration is essentially a horizontal arbor press which has been elongated to accept driveshafts up to 8 feet in length. This machine press-fits end pieces such as tube splines or yokes to the driveshaft tube prior to welding of such end pieces to the tube.
Prior art driveshaft rebuilding machines often were unable to maintain an accurate common centerline between the end pieces and the tube throughout the pressing operation. During the pressing operation on some prior art machines, the components moved relative to one another. While the end pieces were restrained radially by friction, the tube was free to float radially as well as longitudinally. This undesirable radial motion often resulted in a radial misalignment which is commonly termed "run out". If the radial misalignment was extreme, splitting of the tube sometimes resulted.
When using such a prior art push-up machine, removing excessive run out before the welding operation required extensive straightening, which, of course, added to the overall time and cost of rebuilding a driveshaft.
The end pieces are held in tooling or fixtures. Because a rebuilding operation deals with many difference sizes of driveshafts and end pieces and also with difference styles of end pieces, many prior art machines did not include fixtures which placed the end pieces on a common centerline relative to the tube, thus resulting in run out as mentioned above. In some prior art machines, all U-joint end pieces were required to be disassembled prior to installing such end pieces to the driveshaft tube. In these operations the tube yoke only was installed. The spline yoke or flange yoke and the journal cross were removed. Because of this fact and because the machine operator did not have any mechanism for establishing a common center between the tube and the end pieces run out often occurred.
Under actual vehicle operating conditions, driveshafts normally run with a U-joint at each end. The standard U-joint consists of two opposing yokes mutually joined by a journal cross. When the driver yoke rotates at a constant speed, the adjoining driven yoke undergoes a final sinusoidal speed variation proportionate to the degree of joint flex. These fluxuations may be minimized by orientating the driver yoke at one end relative to the driver yoke at the other end of the tube. This technique is well-known and is called phasing.
Many prior art push-up machines depended upon operator judgement in setting up the phase of end pieces such as opposed "U-joints". The U-joint at one end is usually mounted on a spline shaft, while the other U-joint is mounted directly to the shaft tube. The push-up machine pressing operation normally involves installing a tube spline at one end and a U-joint at the other end. To obtain proper phasing, the U-joint at one end must be coordinated and aligned with one of the spline teeth at the other end. Often, tube blanks and small spline diameters also combine to make manual phase alignment, done by individual operators, relatively inaccurate.